The present invention relates to a high frequency converter circuit for converting a differential output signal from a differential amplifier to a single-ended output signal and, more particularly, to a high frequency, i.e., frequencies above eight hundred (800) MHz, circuit and method for combining differential output signals into a single-ended signal and simultaneously achieving an impedance match from the differential amplifier and the input of a single-ended output stage.
In many high frequency communications systems it may be necessary to convert differential output signals from a differential amplifier into a single ended signal. For example, in some wireless telephone communication systems operating near or at 900 MHz there is a requirement that a single ended transmission signal be utilized to drive the antenna for transmission. However, typically, differential signals are utilized which requires a converter circuit to derive the single ended signal before it is applied to an input of a single-ended output amplifier stage prior to driving the antenna. Matching of the output impedance of the converter circuit to the input impedance of the output amplifier stage is also required.
In a known prior art differential to single-ended converter one side of the differential outputs of the differential amplifier is simply thrown away, being coupled to ground, while the other output is coupled to the input of the single-ended output amplifier stage. This technique suffers from several disadvantages such as low gain, poor isolation, to name a few. Moreover, the use of an inductor is relatively expensive wherein production cost are desired to be maintained as low as possible.
Hence, a need exists for a low cost improved differential to single-ended converter for converting high frequency differential signals to a single-ended signal and simultaneously achieve impedance matching to a following single-ended stage while eliminating the disadvantages mentioned above with known prior art circuits.